Ricin is one of the most deadly naturally occurring poisons known. Victor Cohen, director of pharmacology in the department of emergency medicine at Maimonides Medical Center in Brooklyn, N.Y., and experts at the Centers for Disease Control and Prevention and elsewhere provide information about the dangerous toxin.

Q: Where does ricin come from?

A: It is found in all parts of the castor bean plant but is concentrated in the beans and in the mash left over after the beans are processed to make castor oil. Castor oil, which does not contain ricin, is used in making lubricants, paints and varnishes and is an old-time remedy for constipation. The plants are commonly used in gardens and grow like weeds along riverbanks and stream beds in the southwestern USA.

Q: How does someone get exposed to ricin?

A: It can be turned into a powder, mist or pellet. It also can be dissolved in water. Ricin can be inhaled, ingested in food or water, or injected. It can also cause skin irritation or rash when it comes in contact with skin. Workers in castor oil manufacturing facilities have had such skin exposures. No ricin deaths are known to have been reported in recent years.

Q: How is ricin poisoning treated?

A: There is no antidote, so doctors provide breathing assistance, intravenous fluids and other supportive care. For ingested ricin, doctors can flush out the stomach with activated charcoal to absorb the poison. If a patient survives through the first three to five days, full recovery is likely.

Q: How much ricin is enough to cause harm?

A: A 500-microgram dose, about the size of the head of a pin, is enough to kill an adult by injection. The CDC says larger amounts of ricin would be needed to kill someone by inhalation or ingestion, but it doesn't specify the amount. Other sources estimate that 1 milligram of ricin ingested, or 30 micrograms per 2.2 pounds body weight inhaled, would be lethal.

Q: Isthere a legitimate use for ricin?

A: It is used in research. Because it is so effective at killing cells, it is being studied for use as a potential treatment for cancer.

Q: Is it against the law to have or make ricin?

A: There are legal uses for castor bean plants, and scientists are permitted to possess small amounts of ricin for research purposes, but there have been prosecutions under the Biological Weapons Anti-Terrorism Act for illegal possession of ricin powder.

Q: Can anyone get a hold of ricin?

A: Scientists say that anyone with an undergraduate degree in chemistry has the necessary knowledge to extract ricin from castor bean mash.